1. Field of the Invention
The present invention relates generally to communication network management, and more particularly to a method and system for allocating traffic demands in full duplex, ring topology networks.
2. Description of the Prior Art
Traditional metropolitan networks have been designed for voice rather than data services using circuit-oriented technologies such as Synchronous Optical Networks (SONETs). Because SONET-based time-division multiplex (TDM) networks are typically deployed over fiber rings, much of the existing fiber plant in metropolitan areas is in ring form. Ring topologies enable SONET to implement a fast (e.g., sub 50 ms) protection mechanism that can restore connectivity using an alternate path around the ring in case of fiber cuts or equipment failure. The rapidly increasing demand for data traffic, however, is challenging the capacity limits of these existing transport infrastructures. This is compounded by the fact that SONET-based networks generally utilize available bandwidth inefficiently. Specifically, SONET was designed for point-to-point, circuit-switched applications, where each circuit is allocated a fixed amount of bandwidth that is wasted when not in use. Such fixed allocation puts a limit on the maximum burst data-transfer rate between endpoints, which is a disadvantage for data traffic because data traffic is inherently bursty. In other words, traffic may flow intensely between two devices and then stop abruptly.
With advances in packet-oriented technologies such as Optical Gigabit Ethernet technology, which is capable of supporting fiber spans of large distances, Ethernet technologies have emerged as a viable alternative for data transport in public networks. As nearly all data packets begin and end their trip across the Internet as Ethernet frames, carrying data in a consistent packet format from start to finish throughout the entire transport path eliminates the need for additional layers of protocol and synchronization that result in extra costs and complexity. In addition to efficient handling of IP packets, Ethernet has the advantages of familiarity, simplicity, and low cost. Despite these benefits, Ethernet switches rely on Ethernet bridging or IP routing for bandwidth management. Thus, while Ethernet switches can provide link-level fairness, this does not necessarily or easily translate into global fairness.
Consequently, neither SONET nor Ethernet effectively manages a shared resource such as a fiber ring shared across thousands of potential subscribers. More particularly, the network is underutilized in the case of SONET and non-deterministic in the case of Ethernet.
One emerging solution for data transport applications is Resilient Packet Ring (RPR) technology, a network architecture and technology designed to meet the requirements of a packet-based data traffic. It provides features typically associated with SONET—efficient support for ring topology and fast recovery from fiber cuts and link failures—while at the same time, providing data efficiency, simplicity, and cost advantages that are typical to Ethernet.
Generally described, RPR is typically implemented on two cross directional loops (or one bi-directional ring) connecting each RPR device, or node. At each node, traffic that is not destined for the node simply passes through and does not get queued and scheduled. FIG. 1 illustrates an exemplary ring consistent with conventional RPR topology having four nodes: 110a, 110b, 110c and 110d. Each of these nodes may be aware of the location of each other node via a topology discovery protocol. For example, node 110a may be aware that node 110b is one segment clockwise and three segments counterclockwise from node 110a. The traffic demands on the ring are allowed to be routed on either side of the ring, and capacity for all spans of the ring may be required to be equal. Conventionally, when a traffic demand is to be originated from a particular node, the node selects the direction that requires the shortest transit path to the destination (i.e., the smallest number of links) and then inserts the traffic in that direction. Bandwidth is only consumed on the traversed segments.
However, RPR rings are still subject to becoming poorly routed. As traffic demands are provisioned and de-provisioned, certain spans of the ring may become congested while other spans become under utilized. By actively managing the traffic demands within a network, overall utilization may be increased and the need for adding new capacities to the network may be decreased. Therefore there is a need for a method and system of optimizing the routing of traffic demands for efficient utilization of network capacities.